Search lines made from rope are typically used by firefighters to stretch into a building as a safety line when there is heavy smoke and poor visibility. A firefighter can follow the search line out of the building if there is an emergency. The traditional system is fairly simple but has various drawbacks.
The search line is initially extended by a lead firefighter, who is normally equipped with full protective gear, SCBA and/or a thermal camera. The lead firefighter (officer, team leader) ties the search line rope to a sturdy object at the entrance of an area to be searched. Some rope may have pre-tied overhand knots approximately every twenty or twenty-five feet. The knots provide indication to the firefighter how far they have traveled into the area to be searched. Typically a single knot is tied to mark twenty-five feet, two knots to mark fifty feet, three knots for seventy-five feet, etc. This may continue to seven knots at one hundred seventy five feet or more.
It can be fairly tedious and somewhat complicated to correctly set up a search line in this manner. In addition, the knots do not provide the firefighters directional indication pointing to the entrance/exit if the firefighters become disoriented in dense smoke. Thus, in some systems additional knots or rings are added to provide directional indication. Having so many knots tied in the rope can cause jams when the rope is deployed from a typical rescue bag with a payout hole. A typical quick-deployment rope bag is disclosed by U.S. Pat. No. 6,880,702 to Colorado.
Finally, firefighters, usually two, each has a second short line called a tag line. The tag line is usually fifteen to twenty five feet long and is tied to the main search line at preset intervals so the firefighters can search within the radius of the tag line. In a typical setup, the officer/team leader ties large loops at set locations so the tag-line searchers can lock into and search in a set pattern off the main search rope. In summary, this typical search line system can be labor intensive, inefficient and confusing, leaving room for improvements.